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1. OBJECTIVES
1.1 To realize Magnetic Resonance Imaging studies with T.S.E
(TURBO SPIN ECO) and three-dimensional Reconstruction in prelingual
patients having deep neurosensorial hypoacusia.
1.2 To realize Magnetic Resonance Imagenology studies with
T.S.E and three-dimensional Reconstruction in those patients having
normal audition that will be the control group.
1.3 To evaluate in the images obtained the Morphology of
the cochlea - semicircular channels and vestibule, acoustic-facial
package, vascular structures of the IAC ( INTERNAL AUDITORY CANAL).
Morphology and dimensions of the cochlear and vestibular aqueducts.
2. PURPOSES
2.1. To establish an
imagenolic type diagnostic method that will enable us to evaluate in a
more reliable way those patients having deep bilateral neurosensorial
hypoacusia.
2.2 If possible, to look for the etiological cause, responsible
for the deep neurosensorial hypoacusia in those patients whose
etiology has not been determined and due to this their hypoacusia has
been denominated as idiopathic.
3. THEORETICAL
FRAMEWORK
Patients with otoneurologic
symptoms such as progressive neurosensorial hypoacusia, tinnitus,
vertigo, sudden deafness and fluctuating hypoacusia undergo many
clinical, para-clinical, audiological, neurophysiological and
imagenologic studies, with the purpose to obtain better diagnostics
each time; however, no matter the efforts, the diagnoses we do today
don’t get to the ultimate cause.
The study of the internal ear is made by parts, according to its
components.
The high resolution CT is the method of election for studying the
anatomy and the alterations of bony labyrinth (2); in the functional
part, we study the integrity of the neurological via and the proper
functioning of the sensorial organ, through audiological and
neurophysiological analyses(1,2); which suggest the location of the
lesion and the affectation level of the function, without showing us
the defect physically.
During the past decade, the development of the imagenologic techniques
has enabled us to study the anatomy and the pathology of soft tissue
structures in vivo, cerebellopontile angle cisterna, and in general
the pathway of the auditive
via, using MRI. In the last two years, better technological modalities
that allow us to visualize in three dimensions the membranous
labyrinth, the endolymphatic and the cochlear aqueducts, the
different ramps and even the endocochlear liquids have been developed,
offering a better opportunity to find and to clarify the pathology
that affects the patients having symptoms such as neurosensorial
hypoacusia, vertigo and tinnitus, improving the treatment
possibilities. For the congenital malformation cases, lesions of the
petrous apex, mixed deafnesses, or studies for cochlear implant, the
MRI and the CT are complementary studies.
The technological modality that we used in our study was developed by
General Electric in 1.994 and was denominated 3D-TSE. It uses a turbo
image sequence with no echo with continued 0.7 mm or overlapped 1.5 mm
cuts that enable to obtain the image of many previously invisible
structures. For example, the endolymphatic aqueduct can be visualized
in 50 – 73% of the studies, always being visible in the pathologic
dilatation cases (It must not have a diameter greater than 1.5 mm).
In 96% of the studies, the cochlear aqueduct; the trifurcation of the
vestibulocochlear nerve; the facial nerve differentiation in the IAC,
the AICA (ANTEROINFERIOR CEREBELLAR ARTERY) vascular loop in the
cerebellopontile angle or in the IAC; the tympanic and vestibular
scales and the cochlear duct in the different rounds of the cochlea;
the Reissner’s membrane;
the lamina spiralis; the basilar membrane; the Corti’s organ; the
three semicircular channels with their ampules; and the vestibule, in
which the utriculus and the saccule are confused. (7,8,10,11,13).
The importance of the 3D techniques is grounded in the anatomic
identification of very little structures as it was stated earlier and
its applications are:
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Congenital anomalies: They go from dysplasia to aplasia of the
components, limited in some ocassions to the membranous labyrinth,
with a normal CT. The cochlear hypoplasia usually may exist associated
with vestibule or semicircular duct dilatation, in which the labyrinth
size and permeability must be studied and the size of the cochlear
nerve must be estimated.
Vestibular and semicircular duct dysplasias may also exist with a
greater engagement of the lateral duct due to it has been considered
the last embryologic structure to be made. Estenosis or IAC (INTERNAL
AUDITORY CANAL) dilatation may also be seen associated with
perilymphatic fistulas and it is described in the Gusher’s syndrome
(8).
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Trauma: MR makes objective the interval and the extension of the
secondary fibrosis to the labyrinthine contusion throughout the
pathway of the fracture.
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Bacterial labyrinthitis: They are associated with a decrease of the
liquid signal in T2 sequences
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Cochlear preimplant assessment: The image study must predict the
cochlear permeability before surgery; the dimorphic changes of the
internal ear must be detected also. In this case the CT allows a
chartography of the bony labyrinth and the petrous; it searches for
anomalies of the round window and the membranous labyrinth
calcifications showing the cochlear ossification, some labyrinth
malformations and traumatic deformations. The 3D-MRI has a very
important place; it shows the labyrinthine fluid much clearly and it
may predict the cochlear fibrosis before the ossification, being much
more sensitive to detect these types of anomalies, providing
information about the state of the endolymphatic and perilymphatic
liquids. Several times, alterations are not detected, mainly in those
patients who have progressive idiopathic hypoacusia, ototoxicity or
acute deafness (23, 24, 25).
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Vertiginous syndrome study: Not always the central or peripheral
origin of vertigo may be identified, the first examination that the
patients must go through is a study by MR that shows a central lesion
( stem, cervico-occipital junction), a peripheral cause (cerebellopontile
angle, acoustic-facial pedicle) or an engaged membranous labyrinth (expansive
or inflammatory). It must include all the noted sequences, the 3D-MRI
and AMR (Angiography by Nuclear Magnetic Resonance) in case of
vascular loops suspicion or caliber or encephalic vessel flow
anomalies (26).
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Sudden Deafness: It has many origins. Usually, nothing is found, but
it may be helpful in order to discard other alteration. (8).
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Pathology of the Content of the IAC: The use of T2 millimetric cuts
allows the identification of neurinomas with an approximate diameter
of 1 mm, which are usually asymptomatics. The usage of gadolinium in
the neurinomas’ search is not justified except when looking for an
inflammatory pathology of the nerve or of the concomitant labyrinth.
Only 1% of the patients with neurosensorial deafness has an acoustic
schwanoma, 85% of which are born in the vestibular branch, more than
95% are solitaires. In T2-TSE sequence it is present a neurinoma with
a hypointense lesion throughout the nervous axis and the relationships
between this and the bottom of the IAC must be studied. These TSE
sequences are very precise in the diagnosis of 98% of 2mm tumors, and
must be used in those patients who have unilateral symptoms such as
progressive neurosensorial hypoacusis, unilateral tinnitus and sudden
deafness.
In some very small acoustic tumors it is possible to find the nerve of
origin, which has a prognostic value because the ones originated in
the higher vestibular nerve have a greater possibility of preservation
of audition than those that are born in the lower vestibular nerve.
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Vascular loops: In 10% of the patients, the fine cuts confirm the
presence of one normal vascular loop within the IAC.
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Expanded endolymphatic duct and sac syndrome: It is the cause of
progressive deafness during childhood or adolescence, its origin is
unknown. Endolymphatic duct expansion can be accompany by cochlear
and vestibular anomalies. It is a bilateral affection in more than
half of the cases and it is 100% associated with deafness, 33% with
vertigo. Hypoacusis is fluctuating and may become worse with a minor
trauma. It is usually discovered in adulthood so it is very important
the MR study, which is superior than the CT, because it visualizes the
endolymphatic duct and sac directly and it is not an indirect
measurement as the bony vestibular aqueduct measurement is. (10,
28-30)
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Endolymphatic sac tumors: They are responsible for a labyrinthine
dropsy.
- Meniére’s
syndrome and diesase: the endolymphatic dropsy is the clinical triad
of progressive and fluctuating hypoacusis, episodic vertigo and non-pulsatile
constant tinnitus. The Meniére’s syndrome has an identifiable cause (e.g.,
syphilitic dropsy) and the disease is idiopathic. The primary cause of
the volume increase of the endolymph is an unbalance between the
secretion and the reabsorption of the endolymph that could possibly be
secondary to a membranous endolymphatic duct and sac obstruction
located in the vestibular aqueduct. The imagenologic.
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Descriptions have conflictive reports, noting stenotic vestibular
aqueducts (31), the presence of aerial cells around the vestibular
aqueduct, short aqueducts and few mastoid pneumatization.
- No
really useful findings have been made until now but it must be studied
in order to exclude another cause of the symptoms (2).
4. HYPOTHESIS
4.1 3D–MRI enables us to determine or conclude one
etiological cause of structural type in some of such patients with
deep idiopathic bilateral neurosensorial hypoacusis.
4.2 3D-MRI is a complementary
technique of the computed tomography, which is useful for the
diagnosis of patients having deep bilateral neurosensorial hypoacusia.
5. MATERIALS AND
METHODS
Sixty six persons were
prospectively studied as a whole (132 internal ears), 7 subjectively
healthy and 59 patients who had a neurosensorial deafness background,
from the “Instituto Nuestra Señora de La Sabiduría para Niños Sordos”
(Our Lady of Wisdom – Deaf Children Institute) between the ages of 9
and 22 years, assessed by two otologists and to whom a recent
audiometric study had been practiced.
The otologic evaluation included a complete cross-examination and an
exhaustive physical exploration. The audiologic study included tone
audiometry and logoaudiometry, with the purpose of establishing the
type of hypoacusia present in the patient.
In all of them a comparative MRI study of both ears was made in a
superconductive clinical image equipment by IT (Philips Gyroscan
10-NT), with an antenna of a circular surface of an 11 cm diameter
opening (C3), centered on the meatus of the external auditive channel.
At first we used a T1 sequence for localization in the coronal plane
followed by radio frequency turbo type pulse spin echo potentiated in
T2 sequences, with fine cuts overlapped in the axial plane, whose
general parameters were: Tr 9000-11000 mseg, TE 600 mseg, 40 cuts with
a cut width of 1.5 translapped mm with a –1 mm interspace, FOV 130
mm, RFOV 80%, matrix of 256X256,3 acquisitions (NSA) and a total
acquisition time of 6:29 minutes in each ear. All these images were
photographed and analyzed separately as well as the subsequent three-dimensional
reconstruction using the algorithm standard of maximum intensity
projection (MIP) of the coronal plane to the transversal plane with
15 radial images.
The findings were compared subsequently with the clinic and previous
studies such as the CT in every case.
In all the studied internal ears it was analyzed the identification or
not of the anatomic structures of the original images and of those
rebuilt images (MIP).
The following parameters were evaluated during the study:
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Cochlear morphology
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Vestibule and semicircular channels morphology
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Evaluating each one of the three channels, the presence or not of
vestibular expansion.
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Vestibular and cochlear aqueduct’ diameter.
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Expansion or not of the endolymphatic sac
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Acoustic-facial package morphology.
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Vascular structure visualization of the IAC evaluating them at the
acoustic pore and the cerebellopontile cistern levels.
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IAC morphology.
6. UNIVERSE AND SAMPLE
Two groups of patients were
chosen: A first group constituted by 7 healthy patients, who had
completely normal audition, with no personal nor family hypoacusia
background, average age of 20. This will be the control group.
The second group is made up of 59 patients with deep bilateral,
acquired or detected before the age of 5, neurosensorial hypoacusia.
The age of these patients goes from 9 to 22 years.
The two groups of patients had made an imagenologic study in both ears.
7. RESULTS AND CASE PRESENTATION
The obtained results from this study must be carefully analyzed.
We believe that this technique has opened a window towards clarifying
some of the pathologies that were unknown until now and that are very
important to diagnose.
It is important to clarify that these 66 patients with deep bilateral
neurosensorial hypoacusia had previously undergone a high resolution
computed tomography and it had been reported as normal.
The first obtained data is the percentage of abnormal imagenologic
findings by 3D-MRI in those patients having deep bilateral
neurosensorial hypoacusia. Finding that 59 patients having deep
neurosensorial hypoacusia, with previous CT reported as normal, the
abnormal findings by 3D-MRI were in 13 patients (25 ears) which is
equivalent to 22%. (Table No. 1).
From the 12 patients having neurosensorial hypoacusia due to
meningitis, in two patients the obliteration of the membranous
labyrinth is evident (4 ears) 14%, in the rest of the patients there
was no alteration (Table No. 6).
PRESENTATION OF CLINICAL CASES
Next we present the images obtained from three patients with no
pathology (photos 1,2 and 3) in which all the structures of the
internal ear may be seen in great detail.
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A patient with bilateral malformation of the internal ears. In the
right side the higher vestibular branch of the vestibulocochlear nerve
may not be identified, the vestibule is small, only one of the endings
of the semicircular duct may be identified. In the internal ear the
IAC is stenotic, in its interior no nervous structure may be
identified, the vestibule and the posterior and upper semicircular
ducts are dysplasic and the lateral semicircular duct may not be
identified either (photos 4 and 5).
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Two cases of endolymphatic duct and sac expansion syndrome in three
patients. One was 10 years old and had symmetric bilateral expansion;
both were men, the first one had deafness attributed to ototoxics (Kanamycin)
and the second one had complete progressive right deafness and 75% in
the left side (photo 6).
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A 22 year old patient with neurosensorial hypoacusis in whom the
cochlear apex could not be seen and only one ending of the posterior
semicircular channel on the engaged side was visible, having a normal
CT and a normal contralateral study (photo 7).
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A 6 year old girl patient who had deep congenital right deafness of
unknown etiology to whom in the engaged ear we may see the stenotic
IAC and the nervous branch may not be identified, with no other
associated alterations and a normal left ear (photo 8).
8. DISCUSSION
The results of the imagenologic studies in the patients with
neurosensorial deafness show great variations and only in a few cases
they have identifiable anomalies. The direct visualization of the soft
tissues, the internal ear, and the membranous labyrinth liquids
including the endolymphatic duct and sac in MRI that include 3D-TSE
sequences is higher to the CT of the temporal bone which only
identifies the channels of the bony labyrinth; the MRI plays a
preponderant place in the identification of the anatomy and
pathologies of the membranous labyrinth and the associated neural
structures, being MRI an essential complementary study to delineate
the structural anomalies of the internal ear, even though, as it is
described only by a low percentage (18.4% in our study) of the
patients having neurological deafness show internal ear alterations,
being of the membranous labyrinth associated or not to bony labyrinth
malformations and vestibulecochlear nerve aplasia, a finding that
counter indicates the positioning of a cochlear implant.
These sequences with infra-millimetric cuts potentiated in T2-TSE are
also the choice for studying those patients with suspicion of the
membranous labyrinth obliteration usually secondary to chronic
labyrinthitis from a different etiology including luetic, viral,
autoimmune as the Cogan’s syndrome; bacterial of thympanogenic,
meningogenic, hematogen or posttraumatic origin since these may
predict the cochlear fibrosis before the visible ossification by CT.
This technique must be attached to the cochlear permeability study in
the patients chosen for cochlear implant, with repercussion in the
type of implant and the surgical technique that will be used.
It is also the chosen examination to identify and characterize those
young patients with endolymphatic duct and sac expansion syndrome with
hypoacusis, or unilateral or bilateral neurosensorial deafness,
allowing also the identification of membranous labyrinth dysplasias
that may be associated with this syndrome and displacing the CT that
was the method of choice for the diagnosis of the Vestibular Aqueduct
Expansion syndrome, as previously known.
In cases were there is a neurovascular compression suspected that
usually presents with a hemifacial spasm, trigeminal neuralgia,
vertigo and tinnitus with or without associated neurosensorial
hypoacusis. This new T2-TSE sequence with complementary AMR are the
chosen methods to establish these loops, which are described as
“normal” findings in asymptomatic patients.
It must also be practiced to patients with clinical retrocochlear
lesion impression in IAC and cerebellopontile angle, who present a
clinical frame of unilateral or
asymmetric neurosensorial deafness associated to tinnitus, vertigo and
altered or not audiologic tests.
In grown up patients with initial high tone engagement and bilateral
symmetric hypoacusia NS, the first possible diagnosis is the
Presbyacusia, but an overadded cause such as dolichoectasia of the
basilar artery, compressive loops, acoustic trauma or other treatables
causes such as an acoustic schwanoma must be dumped, more over if
there is asymmetry in the hypoacusia or deafness. In our series we
did not find any case of retrocochlear tumoral lesion.
In acute deafness cases this study must also be used because up to 20%
of the acoustic neuromas cases present this type of deafness. In our
case we could visualize cochlear apex obliteration and partial
obliteration of the posterior semicircular channel in the ear that is
correlated with the clinic frame of sudden right deafness associated
to vertigo and homolateral lateropulsion but we can not prove that it
is not an accidental finding.
The visualization of the endolymphatic duct and sac is difficult, it
was only visualized in 42.5% so it is impossible to correlate the non
visualization (53.8%) with the diagnosis of Meniére disease, as it
has been stated by some authors (31).
In our study, we obtained an excellent identification of the anatomic
structures; we reported the cases in which we found evident
alterations in the 3DT2-TSE sequences using inframillimetric cuts, in
agreement with those found in the literature, we introduced such
sequences in the study of those patients having
clinical suspicion of the membranous labyrinth, acoustic-facial
nervous package and auditive via pathology.
It doesn’t exist, nor is this a study of the method sensitivity and
specificity, that would be ideal, but it is not possible to correlate
surgically the findings in all the cases because they are not usually
surgically treated and during an implant not all the described
structures may be visualized. However, it is a very useful technique
that in some occasions may be used alone but generally it must be part
of a complete study of MRI including some other sequences such as the
potentiated in T1 before and after the contrast, potenciated study in
T2 of the encephalon, AMR, and even high resolution CT.
9. CONCLUSIONS
9.1 The 3D-MRI allows the visualization of the internal ear
structures and also the detection of internal ear alterations that may
be responsible for the deep NSH.
9.2 The high resolution computerized tomography with axial
and coronal cuts, and the 3D-MRI are very important imagenologic
studies in the diagnosis of deep NSH and we may not disqualify the
computerized tomography because we consider that both studies are
complementary.
9.3 In about 55% of the patients having idiopathic deep
NSH, it was possible to determine some type of structural alteration
of the internal ear or IAC that could explain the hypoacusis.
9.4 The expanded vestibular aqueduct syndrome is an
etiology that must be considered in the diagnosis of the idiopathic
deep NSH and the alteration might be detected by 3D-MRI.
9.5 In those patients having secondary deep NSH to
meningitis it is feasible to detect, near 14%, membranous labyrinth
obliteration.
9.6 It is necessary to gain more experience in the
interpretation of the 3D-MRI with the objective of detecting some
other pathologies that up to now are unknown. |
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